In larger buildings, traffic structures like e.g. tunnels and ships evacuation times can be 30 minutes or more. Therefore these structures are typically equipped with electrical emergency devices which have to be supplied with electrical energy at least during the evacuation time period in order to facilitate an evacuation. These are e.g. smoke extraction blowers, emergency lighting and placards, etc.
The suitability of an electrical installation for power supply also under the effect of a fire is designated as circuit integrity. Circuit integrity is defined by different standards. E.g. cables are being loaded with a voltage according to the standard IEC 60331-11/-21/-23/-25 and exposed to a temperature greater than 750° C. for 90 to 180 minutes under the effect of a flame. After some time the strand insulations of the cable lose their insulation capability under the flame effect and the strands of the cable short out. This means a functional breakdown. The behavior under this test is designated through “FE” with information regarding the duration of circuit integrity in minutes. A cable that maintains circuit integrity under this test e.g. for 90 minutes is designated as “FE 90”. Similar standards are BS 6387 cat. C and VDE 0472-814. Other standards relate to circuit integrity of cables under the impact of fire and water which e.g. is intended to represent the effect of sprinkler systems in case of a fire, thus e.g. DS 6387 cat. W and VdS 3423. Other standards relate to circuit integrity of cables under the effect of fire and mechanical impacts which is e.g. intended to simulate the effect of components falling onto the cable as it often occurs during a fire, thus EN 50200, EN 50362, and ES 6387 cat. Z. Besides that there are standards which relate to circuit integrity not only of cables but of entire installation systems. This is also designated as system circuit integrity. System circuit integrity, besides the cable, includes supporting elements like cable fasteners, cable suspensions and cable guides and electrical connection elements like branch off- and connection devices since they all together assure circuit integrity of an entire installation. A standard relating to system circuit integrity is e.g. DIN 4102 part 12. For a test according to this standard, flame application and heat up of an entire installation is performed over a length of 3 m according to a particular rising standard temperature curve which initially has a steep slope and then becomes flatter and flatter until it reaches approximately 900° C. after 90 minutes. The behavior under this test is represented by “E” with a statement for the duration of the circuit integrity in minutes. Thus, “E 90” represents system circuit integrity for 90 minutes.
Typical cables do not comply with circuit integrity requirements of this type since the strand insulation can melt off or burn off rather quickly under fire influence and a short circuit can then occur through conductors contacting one another. In order to prevent a short circuit particular devices like particular strand insulations are required. Generally obtaining higher circuit integrity durations is technically complex. The same applies with respect to the relatively high requirements which are placed by the system circuit integrity standards upon support elements and connection elements.